1. Field of the Invention
The present invention relates to a spiral spring arrangement useful for general measuring instruments, and, more particularly, to a spiral spring arrangement using two spiral springs.
2. Description of the Prior Art
A known spiral spring arrangement for instrument use such as, for example, a damping spring for induction disk type relays, has hitherto been constituted essentially of one spiral spring having its outer end connected to the frame work of the relay, and its inner end connected to the rotating shaft of the induction disk.
The damping spring plays an important role in determining the starting point of a relay, and is often used, for example, to set the operating point of a relay. In order to realize a high-sensitivity relay, the damping torque of the spiral spring used must be sufficiently small. It is desirable that this small damping torque be determined to be an arbitrary value over a wide range when sensitivity adjustment is needed. To this end, the spring constant should be reduced by suitably determining the cross-sectional geometry and the material of the spring, and the winding angle on the spring should be arbitrarily determined over a wide range. Presently, however, the prior art is unable to provide a spiral spring arrangement permitting adjustment of sufficiently small damping torque over a wide range because the spring constant cannot further be reduced by simply modifying the cross-sectional geometry of the spring or by choosing the material of the spring. From an electrical point of view, there are limitations on the use of a spiral spring as a current path. If a satisfactory spring constant could be achieved by sufficiently thinning the spring strip and reducing the cross section thereof, the spring will be mechanically weak and so delicate that extra care is required when it is handled or installed in position. In addition, because the spring is too thin, the angular displacement cannot easily be modified for sensitivity adjustment for the associated relay. Furthermore, such a weak spring is very liable to become extended or entangled even by faint vibration with the result that the spring loses its normal function and introduces various undesirable effects into the associated instrument.